Oxidizer for black liquor



Oct. 9, 1951 o. KRESS 2,570,460

OXIDIZER FOR BLACK LIQUOR Filed Oct. 19, 1948 wmzw ATTORNEYS.

Patented Oct. 9, 1951 QOtto Kress, Appleton, Wis.,assignor to The Institute of Paper Chemistry, Appleton, Wis., a corporation of Wisconsin Application October 19, 1 94s,seria1uo.55.35-5

3 Claims.

The presenttinvention .relatesgenerally to imsprovements pertaining to the art of pulp production, and re1ates=morespecifically to improve- :ments in the mode of handlingblackdlquorsuch :as is recovered in-kraft pulping.

I- he primary object of emy present invention is -to provide improved apparatus for treating vchemical solutions-such as black liquor, in order to increase their-sulfidity and toavoid escape of :hydrogensulfide.

'Whenmanufacturingpulpby the kraft process, atzthe end of the cooking .-procedure most=of the caustic soda hascbeen consumed but about one- :lia-l-f of the original sodium sulphideoriginally present in the cooking liquor remains. The .resulting liquor which is separated from the pulp 'bysui-tabl'e washingisz-knownas black liquor, and --this black liquor is #now evaporated with well known equipment to produce a .concentrated sliquor of approximately sixty .per .cent concen- "tration. This concentrated liquor is burned in :a furnace forthe-recovery of sodium compounds land-steam is produced by the combustion of the organic portion ofethe black liquor. Duringsuch concentration of the weak 'black liquor 'to the -strong black liquor and which is accomplished in multiple effect evaporators, considerable hy- =drogen sulphide is produced and lost, this being objectionable not only irom the standpoint of lossofsulphur, but .also due'to the contamination of .air and .condensed water delivered -from the .multiple efiect evaporators.

While diverse methods, and equipment for oxidizing the sulphur ,present in the black liquor in -or'derito save sulphur have :he'retofore been proposed, most of them based upon the provision of extensive surface contact areas between "the liquor and .air beiore the liquor was delivered to "Jthe concentraltors, these prior systems involved "too much agitation of the liquid which would result in excessive and objectionable foaming "espedia'lly'whenres'inous wood had been cooked, and-the prioroxidizing'equipment Would-also tend to become clogged with deposits thereby making 'it "impossible to effectively expose the liquor to the'airand also making it morediificult topropel the oxidizing air through the oxidizing tower. Evehthe mos't efficient prior oxidizing units also failed to cffec't 'su'jficient recovery of sulphur to prevent the productionof .enough hydrogen sulphide to contaminate the water and air in proxirnity to the 'mills, and this contamination .has heretofore 'beenazconstant source of annoyance iirom the standpoint :of .bothxair 1 a'ndstream polluition.

. 2 -.-It.--is thereforeamore-specific object of ithe present 'invention -.to provide an improved mode of subjecting black .liquor to .a now of air ink- .manner whereby objectionable production and escape of hydrogensulphide .is eliminated, and maximum available 7 sulphur .is recovered.

:Another specific object of .this invention is to provide simple and highly .efiective apparatus for treating black liquor :for the recovery of. sulphur and for the elimination .of offensive odors duringthe-recoveryprocedure.

vA-iurther specific object of my invention is .to provide an improved system of oxidizing black liquor automatically and most efficiently, and .in amanner whereby escape .of obnoxious odors and l-lossof valuableehemical-is avoided.

.itower embodying the invention;

in carrying on my improved system,,and of the construction and operation .of a typical oxidizing tower which maybe utilized to exploit thepres- .ent invention, Im-ay he had by referring to the drawing accompanying and. forming a part of thisspecification wherein like reference characters designate the-same orsimilar parts in the various views. I

Fig. .1 is -a somewhat diagrammatic vertical .section through a typical black liquor oxidizing Eig. L2 is an enlargedkperspectwe view of a fragment of the upper interior of the oxidizing .tower s'howninFig. T1,;

Fig. '3 isasimilarly enlarged transverse section through a fragment-atone of the plates or shelves =ofthe unit, 'taken along :the .line 33 ,ofYFig z; :Fig. A .is a likewise enlarged vertical section through'theeooperating ends of two of the successivesuperimposed plates, also showing rifiies applicable to the upper surfaces thereof in order to .gently augment exposure of all portions of .th liquid to the air ;-and Fig. 5 is a similarlyienlarged fragmentary ver tical section through the liquid delivery end of thei-lowermostishelf.

While the invention r-h-as been shownand'described :herein by way of illustration as being especially advantageous for the treatment of black liquor, it is not my desire to unnecessarily limit the utility thereof by virtue of this particular use; and it is also contemplated that specific descriptive terms employed herein be given the broadest possible interpretation consistent with the disclosure.

In accordance with my invention, I expose the black liquor promptly after it is blown or delivered from the cooker in a kraft process pulp mill, in the form of an extensive and relatively thin and uninterrupted film, and for a prolonged period of time, to an abundance of gradually advancing oxidizing air. Violent agitation of the film is constantly avoided, and the oxidizing air is uniformly distributed throughout the entire exposed area of the film while this air is being conducted through the film producing zones with minimum obstruction to the air flow. I also provide simple instrumentalities for permitting rapid lower extremity, and also having an abundant fresh air inlet pipe Il near its lower end and a spent air outlet pipe I2 at its upperextremity; and a series of superimposed oppositely inclined shelves or plates I4, I5 confined and mounted within the tank 8. The tank 8 may be of any suitable size, shape and height, and the number of plates I4, I5 may be varied as desired, in order to produce an oxidizing unit of any predetermined capacity; and the inclined shelves l4, I5 may be either permanently or detachably secured to the tank interior in any convenient manner. This tower or unit is adapted to be interposed between the cooker and the multiple effect evaporator for concentrating the black liquor prior to burning for final soda recovery. 7

The upperend of the uppermost inclined shelf or plate I4 of the oxidizing tower is adapted to receive fresh black liquor I6 from .the cooker through the inlet 9 and a distribution launder or trough I'I extending transversely throughout the entiretank width, and over a dam I8 formed integral with the adjacent shelf and having a smoothly curved liquid cascading surface for conducting the entering liquid in the form of a thin continuous film onto the upper surface of the top plate I4, see Figs. 1 and 2. The lower end of the lowermost inclined shelf or plate I 5 is adapted to deliver the oxidized film of black liquor I6 from its lower extremity over a smoothly reversely curved apron I9 formed integral with the adjacent shelf I5 and likewise having a liquid cascading surface for conducting the treated liquid into a receiving basin 20 formed in the bottom of the tank 8 and communicating with the outlet I which may be provided with a control valve 2| for regulating the depth of liquid within the basin 20, see Figs. 1 and 5. The outlet Il] in turn communicates with the usual multiple eiTect evaporator of the mill.

The successive superimposed shelves or plates I4, I are located closely adjacent to each other and are oppositely inclined only sufficiently to produce a relatively slow and sluggish'flow of the liquid films downwardly therealong, and the plates I4 are all disposed approximately parallel to each other while the plates I5 are likewise disposed with respect to each other. The lowermost end of each shelf l4, I5 except the lowest, is provided with a depending smoothly curved lip 22 which is directed downwardly toward but is spaced from the uppermost end of the adjacent succeeding lower shelf, sufiiciently to provide a horizontal gap between each pair of shelves I4,

I5 and to produce an extensive continuous zigzag film of the descending liquid or liquor I! from the crest of the dam I8 to the basin 20; and the relative inclination and spacing of the plates I4, I5 also creates a foam dissipating chamber 24 of gradually enlarging magnitude extending along eachplate in the direction of advancement of the film therealong, as illustrated in Fig. 1.

The oxidizing air admitted to the lower portion of a tank 8 through the inlet or supply pipe II may be injected by a blower 25 through a series of openings 26 formed in the pipe II, and the air outlet or exhaust pipe I2 may be connected to a suitable vacuum or reduced pressure zone such as an exhaust fan or a stack. In order to permit the oxidizing air to flow freely and with least obstruction through the successive super imposed chambers 24 of the evaporator, without interrupting the continuity of the liquid film flowing along the shelves or plates I4, I5, each of the latter is provided with a raised central inverted trough-like duct portion 21 which may extend throughout the entire length thereof.

' These raised portions 2'1 while being relatively narrow as compared to the overall width of their shelf plates, should have sufiicient area to permit free flow therethrough of all of the air admitted to the unit; and the lower end of the lowermost duct portion 21 should provide an abundant air supply opening 23 directly above the basin 20 as shown in Fig. 5, while the upper end of the uppermost trough portion 21 may be closed at its end 29 above the crest of the dam I8 a indicated in Fig. 1, and the lower end of each of the other raised portions 21 should likewise provide an unobstructed air escape passage or flow opening 30 as depicted in Figs. 2 and 4.

While it is desirable to maintain continuity of the film flowing along the plates I4, I5, it may also be desirable in some instances, to slightly but gently disturb or agitate the film as it proceeds along the shelves beneath the expanding chambers, in order to insure most effective contact of all portions of the liquor I6 with the advancing oxidizing air. Such mild agitation of the liquid film may be effected by applying transverse rifiles or rounded projections 3! to the upper surfaces of the shelves I4, I5 as illustrated in Fig. 4, but these rifiles 3| are preferabl omitted at the zone of transfer of the film from one plate to the next succeeding plate. The riflies 3|. are so formed that they will turn over or roll the successive increments of the continuous film without necessarily interrupting the continuity thereof and without violently agitating the liquid to the extent of producing excessive foaming, but sufficiently to insure thorough contact between the exposed film suriaces and the oxidizing air which spreads out away from the openings 28, 30 and fills the chambers 24.

While the normal operation of the improved oxidizing tower should be quite apparent from the foregoing description of the construction of the apparatus, a rsum of operation will be lower basin. 20.

given. Normally fresh and weak black liquor IE will be: delivered in regulatedquantities through Ether, inlet 9 into the distribution trough 1? from awhence it flows over the dam Hl' in the form .of a: thin. film-a As shown in Fig. 3, this film of liquor-l6- advances slowly along the upper-surnfa'cesof the successive shelves [4,, l5 on opposite :sides of the central raised portions 21, and; as: it leaves; the lower lip 22 of each plate and drops or cascades over the open gapupon the next lower plate, its continuity is preserved, thus causing thecontinuity of the film to be constantly maintained from the time of its formation at the upper dam l8 until delivery thereof into the During this constant flow of the uninterruptedithin. film downwardly through the unit, it may be mildly agitated with the aid of rifile 3|, and as fresh oxidizing air is injected through the supply pipe 5 I, it passes through the lower opening 28 and successively through the upper chambers 24 and through the openings 30, being thus brought into intimate direct contact with all portions of the exposed film surfaces and effectively oxidizing the sodium sulphide to produce sodium salts which may be subsequently readily reduced and recovered in the furnaces.

The fiow of oxidizing air upwardly through the tank 8 and chambers 24 is unimpeded, and the continuity of the film is not disrupted, due to the fact that the air flows from one chamber 24 to another through the central openings 30 afforded by the raised plate portions 21 and does not pass directly through any portion of the film at any point. If foaming of the liquid occurs at the lips 22 or at any other localities, when handling resinous liquor [6, the foam bubbles will be dissipated within the elongated tapered or expanding chambers 24, and the film of liquid effectively retains the sulphur and prevents formation and escape of hydrogen sulphide with the oxidizing air which is eventually withdrawn from the upper outlet l2. The tapered chamhers 24 also serve to spread thgascending air stream throughout the entire upper surfaces of the successive liquid film sections; and the sulfidity of the black liquor I 6 is thus automatically increased without the loss of hydrogen sulphide and the resultant odors and contamination caused by escape of this chemical.

From the foregoing detailed description of my improved procedure apparatus, it should be apparent that the invention provides a simple yet effective system of treating black liquid orthe like for the recovery of sulphur while avoiding production of hydrogen sulphide and resultant loss of valuable chemical. The successive steps of the procedure can obviously be carried on automatically with no attention after initial setting of the control valves, and with the aid of oxidizing air under relatively low pressure. The improved apparatus is also simple and comparatively compact in construction considering its ca-- pacity, and is devoid of filth accumulating pockets so that it may be conveniently cleaned by flushing with fresh liquid when necessary. The use of a series of superimposed slightly inclined shelves or plates I4, l5 disposed closely adjacent to each other in zig-zag formation, makes it possible to provide a tower or unit of large capacity which occupies minimum space and wherein most efficient oxidation is automaticaly efiected. The installation and operation of these units may also be effected at relatively low cost, and the use of my improved system effectively eliminates both contamination of streams by discharging waste chemicals therein, and thespreading of offensive cedure onto the precise details. of construction and? operation of the oxidizing unit, herein shown and described, for various modifications within the scope-of the; appended claims may. occur .to

persons skilled inthe art I claim:

1' An oxidizer for black liquor comprising, a vertically elongated tubular casing provided with superimposed. oppositely inclined shelves the lower end of each of which has a depending lip spaced from but closely approaching the upper end surface of the next successive downwardly inclined shelf to provide a narrow open gap between each succeeding pair of said shelves, means for delivering liquor to the uppermost of said shelves for gravity flow downwardly along said shelves and across said gaps in succession to produce a continuous and uninterrupted downwardly advancing thin film, means for injecting air into said casing beneath the lowermost of said shelves, and an air duct mounted on and extending downwardly along each shelf and being provided with a cut-out portion adjacent to the open gap at the lower end of the shelf, said ducts providing passages for air to rise successively through said cut-out portions and over the surfaces of the adjacent shelves and dividing the continuous liquor film into segregated downwardly flowing stream sections.

2. An oxidizer for black liquor comprising, a vertically elongated tubular casing provided with superimposed oppositely inclined shelves the lower end of each of which has a depending lip spaced from but closely approaching the upper end surface of the next successive downwardly inclined shelf to provide a narrow open gap between each succeeding pair of said shelves, means for delivering liquor to the uppermost of said shelves for gravity flow downwardly along said shelves and across said gaps in succession to produce a continuous and uninterrupted downwardly advancing thin film, means for injecting air into said casing beneath the lowermost of said shelves, and an air duct mounted on and extending downwardly along each shelf and being provided with a cut-out portion adjacent to the open gap at the lower end of the shelf, said ducts providing passages for air to rise successively through said cut-out portions and along the upper surfaces of the adjacent shelves and dividing the continuous liquor film into segregated downwardly flowing stream sections and said upper shelf surfaces being provided with transverse rifiles for gently agitating said stream sections.

3. An oxidizer for black liquor comprising, a vertically elongated tubular casing provided with superimposed oppositely inclined shelves the lower end of each of which has a depending lip spaced from but closely approaching the upper end surface of the next successive downwardly inclined shelf to provide a narrow open gap between each succeeding pair of said shelves, means for delivering liquor to the uppermost of" said shelves for gravity fiow downwardly along said shelves and across said gaps in succession to produce a continuous and uninterrupted downwardly advancing thin film, means for injecting air into said casing beneath the lowermost of said shelves, and. an air duct above and extending downwardly provided with anopening adjacent to the open gap at the lower end of the shelf, said ducts providing passages for air to rise from said injecting means successively through said openings and along the upper surfaces of the adjacent shelves and dividing the continuous liquor films into segregated downwardly flowing stream sections disposed on opposite sides of the ducts.

' OTTO KRES-S.

REFERENCES CI TED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,193,359 Castro Aug. 1, 1916 1,452,253 Nevitt Apr. 17, 1923 2,005,316 Hall June 18, 1935 2,035,920 Pyzel Mar. 31, 1936 2,181,330 Janhunen Nov. 28, 1939 2,258,401 Badenhausen Oct. 7, 1941 2,303,811 Badenhausen Dec. 1, 1942 FOREIGN PATENTS Number Country Date 106,022 Germany Oct. 10, 1899 OTHER REFERENCES Page 217 of the book Modern Pulp and Paper Makingjby Witham, J1. (1942) 

1. AN OXIDIZER FOR BLACK LIQUOR COMPRISING, A VERTICALLY ELONGATED TUBULAR CASING PROVIDED WITH SUPERIMPOSED OPPOSITELY INCLINED SHELVED THE LOWER END OF EACH OF WHICH HAS A DEPENDING LIP SPACED FROM BUT CLOSELY APPROACHING THE UPPER END SURFACE OF THE NEXT SUCCESSIVE DOWNWARDLY INCLINED SHELF TO PROVIDE A NARROW OPEN GAP BETWEEN EACH SUCCEEDING PAIR OF SAID SHELVES, MEANS FOR DELIVERING LIQUOR TO THE UPPERMOSE OF SAID SHELVES FOR GRAVITY FLOW DOWNWARDLY ALONG SAID SHELVES AND ACROSS SAID GAPS INSUCCESSION TO PRODUCE A CONTINUOUS AND UNINTERRUPTED DOWNWARDLY ADVANCING THIN FILM, MEANS FOR INJECTING AIR INTO SAID CASING BENEATH THE LOWERMOST OF SAID SHELVES, AND AN AIR DUCT MOUNTED ON AND EXTENDING DOWNWARDLY ALONG EACH SHELF AND BEING PROVIDED WITH A CUT-OUT-PORTION ADJACENT TO THE OPEN GAP AT THE LOWER END OF THE SHELF SAID DUCTS PROVIDING PASSAGES FOR AIR TO RISE SUCCESSIVELY THROUGH SAID CUT-OUT PORTIONS AND OVER THE SURFACES OF THE ADJACENT SHELVES AND DIVIDING THE CONTINUOUS LIQUOR FILM INTO SEGREGATED DOWNWARDLY FLOWING STREAM SECTIONS. 